This invention relates to methods and apparatus for continuous separation and optional recovery of one or more components of a mixture from a liquid containing the mixture. In particular, the present invention is directed to apparatus and methods for isolation of one or more specific elements, isotopes, ions, complexes and/or compounds from mixtures of similar or dissimilar materials in a manner such that the liquid containing such mixture is treated continuously, and such that the thus-isolated material may if desired be economically recovered.
In co-pending application Ser. No. 07/316,201 filed Feb. 24, 1989, the entire disclosure of which is hereby incorporated by reference, a continuous process for treatment of liquids to remove contaminants therefrom is disclosed. The process comprises a series of discrete liquid treatment stages, in each of which a portion of the liquid is maintained in contact with contaminant removal medium for a predetermined residence time, for example in a sequence of containers.
Movement of all or a portion of the medium used in each treatment stage is generally carried out in a batchwise manner sequentially from container to container.
The flow of liquid in a countercurrent direction may be batchwise or continuous, and is regulated through the use, for example, of weirs positioned between adjacent containers so as to achieve the desired liquid residence period in each container. The flow rate of the incoming waste stream into the treatment system is adjusted with reference to the concentration of contaminant(s) to be removed therefrom and the concentration (volume/volume) of medium in each treatment container so that equilibrium conditions are attained in each discrete container prior to advancing the liquid to the next stage in the cycle. To accommodate influent with particularly high contaminant concentrations or pH values at the extreme ends of the scale, it may be necessary to employ systems wherein the residence times of liquid and of medium in each container are fairly extended. Moreover, because operation of the system is based on the attainment of equilibrium conditions in each container, where the efficiency of contaminant removal using any given medium is low the desired degree of contaminant removal may only be achieved by cycling the liquid through a substantial number of treatment stages. Each container is contemplated as having a fairly large liquid capacity (on the order of at least 1 m.sup.3); thus, a requirement for multiple cycles to achieve the desired degree of contaminant removal necessitates the use either of a substantial number of containers (increasing apparatus cost significantly) or of repetition of the entire treatment in the same system (reducing efficiency of treatment). While no limits are set as to the number of containers in any given system, the exemplary embodiment described comprises 8 tanks, only 4-6 of which are generally dedicated to contaminant removal.
In any event, the process of Ser. No. 07/316,201 is most effective for removal of essentially all contaminants of a given type (for example, metal ions or organic compounds) essentially without selectivity for a particular contaminant. For example, using an ion exchange medium, it is quite practical to remove essentially all metal ions from an aqueous solution upon completion of a typical treatment regimen; on the other hand, it is significantly more difficult in such a multiple container system to achieve selective removal of a single metal ion from a mixture thereof. Therefore, while the process of Ser. No. 07/316,201 provides substantial advantages over known methods for removal of a wide variety of contaminants from liquids, it does not provide an adequate solution in those situations where available media show a relatively low affinity for a particular contaminant and/or selectivity with respect to removal or recovery of a particular material is desired.